Determinants of hip and knee flexion range: Results from the San Antonio Longitudinal Study of Aging

Objective. We analyzed data from the San Antonio Longitudinal Study of Aging, a neighborhood-based study of community-dwelling elderly people, to identify factors that determine the flexion range (FR) of hips and knees. Methods. The FR of hips and knees was measured in a cohort of 687 subjects aged 65 to 79 years. We used multivariate models to examine the associations among the FR of hips and knees, and between these and age, gender, ethnicity, body mass index (BMI), pain and its location, self-reported arthritis, and diabetes mellitus. The functional relevance of hip and knee FR was tested by measuring its association with 50-foot walking velocity. Results. More than 90° of flexion in both hips and both knees was observed in 619 subjects (90.1%). Correlations among the FR of hips and knees ranged from 0.54 to 0.80 (P < 0.001 for Spearman r values). Multivariate analysis revealed a pattern of significant associations between each of the joints and its contralateral mate and ipsilateral partner joints that was consistent for both hips and both knees. Using each individual joint as the unit of analysis, the following variables were independently associated with hip or knee FR in multivariate models: rising BMI and female sex with reduced FR of both hips and knees, a Mexican American ethnic background with decreased hip FR, and knee pain with decreased knee FR. The functional importance of the FR of these two important joints was supported by its significant association with walking velocity in a model that adjusted for age, gender, ethnic background, BMI, and hip or knee pain. Conclusions. Most community-dwelling elderly people have a FR of hips and knees that can be considered functional. The ipsilateral and contralateral hip or knee are significant independent determinants of the FR of each of these joints. Obesity, a health problem potentially amenable to preventive and therapeutic interventions, is a factor significantly associated with decreased FR of hips and knees.